The present invention relates to wireless telephone communication, and more particularly to a wireless communication system with a distributed home location register for tracking mobile units as they move between service areas.
Conventional wireless telephone systems contain several service areas, "zones," interconnected by data and voice networks. A zone may contain several base station transceivers and base station controllers, switching equipment, and a Visitor Location Register (VLR). Each base station provides radio links to mobile terminals serviced by a respective zone.
A switch, attempting to deliver calls to a Mobile Terminal, accesses a Home Location Register (HLR) which identifies the VLR, and hence the zone, where each mobile terminal is currently located. This enables the switch to route calls to the base station currently serving the mobile terminals. The HLR also stores information concerning the services enabled for each mobile terminal and information used to control access by the mobile terminals to the wireless communication system. Thus, the HLR must process updates to mobile terminal location information, updates to subscriber service information, and queries for location of mobile terminals.
The VLR temporarily stores the subscriber data for each mobile terminal currently located in the serving zone. The HLR downloads the subscriber's data to the VLR when prompted by the VLR. Thus, the HLR must respond to these data requests and transmit the information to the VLR. The process of receiving and responding to a request for subscriber's data and downloading the data to the VLR is known as location tracking because the process monitors a mobile terminal's location as it moves between zones.
In conventional wireless telephone systems, a single server, common to all of the zones, has provided the HLR function for the multitude of mobile terminals serviced by the system. The single server architecture is problematic because the HLR must be accessed to register with the system and to terminate the mobile terminal's connection to other callers, and therefore, failure of the HLR results in immediate loss of service to the entire system. Consequently, the HLR has often been a fault-tolerant and expensive machine.
Considering the foregoing, a need exists for a wireless communication system that ensures that the failure of a single node, associated with the HLR, does not cause a loss of service to the entire set of mobile terminals serviced by that HLR.